Code review comment for ~harald-jensas/cloud-init:bug/1806014

> Thanks for sorting this out. One more element here is related to kernel
> defaults; at least on Ubuntu the kernel defaults the interfaces accept_ra
> value to 1; which allows RAs on interfaces that aren't forwarding.
>
> The code below which defaults accept-ra to False is going to break that. I
> would like to suggest that only *if* accept-ra is set in the source config
> (for example in the openstack network_data.json where dhcp6 stateful is
> specified, then it makes sense to include accept-ra: true in the interface
> config.
>
> In the renderers, if accept-ra is *not* defined, I'd like to avoid emitting
> any RA related config at all.
>
> Now that cloud-init handles dhcp6-stateless/stateful; I think we only want to
> enable RA on stateful dhcp6, otherwise we should leave the kernel defaults.
>
> Additionally, ifupdown (eni) can toggle these values as well:
>
> accept_ra [0, 1, 2]
> autoconf [0, 1]

Thanks Ryan, this all makes sense.
I have updated the patch to not just enable if accept-ra: true. But also disable if false. And it should not change the OS defaults if accept-ra is not defined at all.